Dual containment pipes are well known, and are frequently used when transporting hazardous materials, or when a piping system may be subject to extreme temperature variations. Dual containment pipes consist of a set of concentric pipes where the inner pipe, or "carrier" pipe, transports fluid, and the outer pipe, or "container" pipe, will prevent leakage into the surrounding environment in the event that the carrier pipe fails. A further advantage of dual containment pipes is that the air that occupies the space between the carrier pipe and the container pipe also functions to insulate the carrier pipe and the fluid that is flowing through it, which may be desirous under many operating conditions. Also, this space can be filled with foam or another insulating material to further insulate the pipe. Finally, this annular space can be used to house monitoring equipment for monitoring the flow of fluid through the carrier pipe.
In order to effectively control the flow of fluid through a series of joined dual containment pipes, a valve, such as a ball valve or butterfly valve, must be inserted between adjacent dual containment pipes at some point along the pipe string. Known dual containment piping systems utilize a standard valve that is designed for use in conjunction with standard, single pipes, where the inlet and outlet ends of the standard valve mate with the carrier pipes of the adjoining dual containment pipes. Use of a standard valve, however, is insufficient because the single casing within which it is contained provides only a single layer of protection against leakage. Further, because a standard valve mates with the carrier pipes of adjoining dual containment pipes, the container pipes of these dual containment pipes are left open at the adjoining ends, and must be otherwise closed off. Accordingly, it has been a common practice to provide an outer containment housing as an additional layer of protection around the entire valve. This outer containment housing, commonly referred to as a "manhole", often is box-like or cylindrical in shape, and is built so that it surrounds the exposed container pipes of the adjoining dual containment pipes, and also to completely surrounds the valve to ensure that leakage from any of these elements is contained within it. Typically, this outer containment housing has a bolted door or other similar access mechanism that allows access to the valve to control the flow of fluid within the dual containment pipes, or to allow for repair or servicing of the valve.
Although this outer containment housing achieves its intended purpose of containing leaks, it does not provide easy accessibility to the valve that controls the fluid flow, which is particularly important in the event of a hazardous material spill or other emergency situations. Further, routine maintenance or periodic adjustments to the flow are difficult and time consuming when the outer containment housing must first be opened or otherwise physically disassembled before the valve may be accessed. Finally, because any leakage will collect in the bottom of the outer containment housing, workers are often exposed to chemicals or other hazardous materials when adjusting or servicing the valve.